c5load
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Do Airlines Use Their A/C To The Max Performance?

Mon Jan 24, 2011 11:39 pm

With airliners getting heavier and longer range these days, do airlines really max perform their airplanes? Take a couple of the biggest planes nowadays: A380, B777-300ER, and the 747-400. The A380s MTOW is around 1.2 million lbs. Do airlines really try and pack fuel, cargo, and pax to reach that weight? That's the only way it'll make money won't it? That goes for the 77W and the 744

77W: MTOW-775K
744: MTOW-910K

If airlines don't need the fuel for that particular mission, would they try and make up that weight in extra cargo, if it can fit? I guess the point of my question is would airlines want to max out weight on their airplanes all of the time, conditions permitting, or do they try and spare them that for sake of extending life?

[Edited 2011-01-24 15:40:25]
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Flighty
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RE: Do Airlines Use Their A/C To The Max Performance?

Tue Jan 25, 2011 12:01 am

Quoting c5load (Thread starter):
I guess the point of my question is would airlines want to max out weight on their airplanes all of the time, conditions permitting, or do they try and spare them that for sake of extending life?

You'll get a better professional response from our other members. But from my experience, airlines are happy to launch a flight at MTOW assuming the heavy cargo is making money. Otherwise, weight increases fuel consumption, which needs to be justified by the revenue of what is being carried. The MTOW isn't some emergency number; the airplanes are designed to perform for decades being used to the max.

The 744 is known to take off at MTOW (875,000 most often) on long-range routes, limiting its cargo load in the process. This means, they reject cargo that is above the legal capacity of the airplane, after adding the fuel. This is also known as "weight restricted."

I haven't heard too many stories about 77W or A380 being weight restricted. Maybe they do carry a lot of cargo.

Quoting c5load (Thread starter):
If airlines don't need the fuel for that particular mission, would they try and make up that weight in extra cargo, if it can fit?

Sure, if the price is right. An aircraft like A333 has a huge cargo hold. Selling that space makes $$, so long as it pays for the loading and the fuel. It's part of the business model.
 
tdscanuck
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RE: Do Airlines Use Their A/C To The Max Performance?

Tue Jan 25, 2011 4:52 am

Quoting c5load (Thread starter):
Do airlines really try and pack fuel, cargo, and pax to reach that weight?

You don't target MTOW, you target maximum payload. For long routes, this may mean you're at MTOW because you're full of fuel and then you take as much payload as you can. For short routes, you're more likely to hit MZFW first (maximum payload), then just carry the fuel that you need for the mission.

Quoting c5load (Thread starter):
That's the only way it'll make money won't it?

You make money with full payload, and just enough fuel to get you to the destination. That may or may not be MTOW (or MZFW).

Quoting c5load (Thread starter):
If airlines don't need the fuel for that particular mission, would they try and make up that weight in extra cargo, if it can fit?

If it can fit *and* if they're haven't hit MZFW yet. If you're at MZFW, it doesn't matter if it's a 100 mile flight and the tanks are 10% full, you still can't stuff more payload on.

Quoting c5load (Thread starter):
I guess the point of my question is would airlines want to max out weight on their airplanes all of the time, conditions permitting, or do they try and spare them that for sake of extending life?

You want the most profit per cycle you can get. I'm not aware of anyone who limits weight to protect life (the airplane is certified to operate at MTOW for its design life). Almost everybody limits engine thrust to preserve engine life, but the relationship between increased thrust and decreased life is much uglier for engines than for aircraft.

Tom.
 
Mir
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RE: Do Airlines Use Their A/C To The Max Performance?

Tue Jan 25, 2011 5:22 am

Quoting c5load (Thread starter):
With airliners getting heavier and longer range these days, do airlines really max perform their airplanes?

I can't think of any reason not to push their aircraft to the limit. Obviously, which limit that is is going to vary from day to day and route to route. Sometimes it will be MTOW, sometimes MZFW, sometimes landing weight plus fuel burn, sometimes climb restricted weight, etc. But there's always going to be some limit, and if you can fill up to that, why wouldn't you?

-Mir
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FlyASAGuy2005
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RE: Do Airlines Use Their A/C To The Max Performance?

Tue Jan 25, 2011 6:33 am

The CR2 does is daily, albeit horribly . Just the other day, had a flight to MLI I believe. The Max was 48 pax and 48 bags. Only issue was they were booked to 50 and ended up with 46 bags, of which 7 were heavies...
What gets measured gets done.
 
ANITIX87
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RE: Do Airlines Use Their A/C To The Max Performance?

Tue Jan 25, 2011 6:29 pm

Quoting tdscanuck (Reply 2):
If it can fit *and* if they're haven't hit MZFW yet. If you're at MZFW, it doesn't matter if it's a 100 mile flight and the tanks are 10% full, you still can't stuff more payload on.

Does this have to do with max landing weight? Will MZFW always be below max landing weight? If you need 10% of the fuel, why wouldn't you be able to increase payload, other than max landing weight restrictions? Is there a fundamental concept I'm missing here?

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A342
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RE: Do Airlines Use Their A/C To The Max Performance?

Tue Jan 25, 2011 6:52 pm

Quoting ANITIX87 (Reply 5):
Will MZFW always be below max landing weight?

Yes, otherwise that would be a crappy aircraft, having to throw out passengers or cargo before landing!   

In the real world, MLW is MZFW plus at least the required fuel reserve upon landing, mostly more than that.

Quoting ANITIX87 (Reply 5):
If you need 10% of the fuel, why wouldn't you be able to increase payload, other than max landing weight restrictions?

In a nutshell, wing bending moment, which puts loads on the wing-fuselage joint. But others will abe able to explain that one far better than I can.
Exceptions confirm the rule.
 
Mir
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RE: Do Airlines Use Their A/C To The Max Performance?

Tue Jan 25, 2011 7:16 pm

Quoting ANITIX87 (Reply 5):
If you need 10% of the fuel, why wouldn't you be able to increase payload, other than max landing weight restrictions?

A342 is correct with the wing/fuselage joint loading issue. Basically, if the fuselage is too heavy, the wings will start to bend and will eventually overstress. To visualize this, put a pen or pencil in the middle of a piece of paper and then pick up the paper from the edges. You can do this without the paper bending too much. Now put something much heavier (like a cellphone) on the paper and try again. You'll notice that the paper bends a whole lot more. Same thing happens with a light fuselage vs. a heavy fuselage, and the MZFW is there to prevent too much bending moment on the wings, which would show up (since wings are more rigid than paper) as stress on the joint connecting them to the fuselage, above and beyond what the engineers designed it to handle.

This is also why, even if the airplane has fuel tanks in the fuselage, the wing tanks are always filled first - it spreads the weight out more evenly.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
ANITIX87
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RE: Do Airlines Use Their A/C To The Max Performance?

Tue Jan 25, 2011 8:41 pm

Thanks, A342 and Mir. Didn't even think about wing bending being an issue, but it's pretty obvious.

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YYZatcboy
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RE: Do Airlines Use Their A/C To The Max Performance?

Fri Jan 28, 2011 5:14 pm

Landing weight is also an issue. If I load up one of our planes with a full load of people I'll more often than not be landing weight limited before I hit MTOW unless it's a long route. (if I forget about landing weight the Chief Dispatcher will not be very impressed)
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Gonzalo
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RE: Do Airlines Use Their A/C To The Max Performance?

Fri Jan 28, 2011 5:35 pm

Quoting tdscanuck (Reply 2):
You make money with full payload, and just enough fuel to get you to the destination.

I think that can confuse some people... you also need fuel in case you have to divert or hold in pattern while weather improves, Go Around.... Oh... and taxiing to the gate too !!!  
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Flighty
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RE: Do Airlines Use Their A/C To The Max Performance?

Fri Jan 28, 2011 7:04 pm

Quoting Gonzalo (Reply 10):
you also need fuel in case you have to divert or hold in pattern while weather improves, Go Around.... Oh... and taxiing to the gate too !!!

I recently learned that going to Hawaii, an aircraft need enough fuel to make all its diversions (and go arounds etc) assuming 1 engine has failed. At the lower cruising altitude, etc. Not sure if that is more fuel than normal, but it's an interesting thought.
 
YYZatcboy
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RE: Do Airlines Use Their A/C To The Max Performance?

Fri Jan 28, 2011 7:17 pm

we plan for 1 engine out at 10 000 ft.
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Mir
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RE: Do Airlines Use Their A/C To The Max Performance?

Fri Jan 28, 2011 10:08 pm

Quoting Flighty (Reply 11):
I recently learned that going to Hawaii, an aircraft need enough fuel to make all its diversions (and go arounds etc) assuming 1 engine has failed. At the lower cruising altitude, etc.

Not just the driftdown altitude, but also the altitude you'd descend to in case of a pressurization failure (i.e. much lower), as YYZatcboy mentioned. And yes, it is a lot more fuel.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
9V-SPJ
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RE: Do Airlines Use Their A/C To The Max Performance?

Sun Feb 06, 2011 5:54 pm

These aircraft are optimized to operate at or close to MTOW. If they weren't they would have designed them to operate at a lower weight. To operate at or close to MTOW, the wings and fuselage need to be of appropriate strength, and this may include strengthening aspects added to the design. If you weren't going to operate at these limits, why would you add this additional strengthening (if required)?
Same with the engines, why put an insanely powerful engine on the aircraft if you aren't going to utilize the full thrust capability - mainly at takeoff and during engine out situations.
As everyone has said, payload is the key here, but sometimes, you may want to carry fuel in place of pax to reach your MTOW. In that case, economically, the fares or cargo carriage prices would be adjusted such that you are still making money on the route.

My two cents  

9V-SPJ
 
YYZatcboy
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RE: Do Airlines Use Their A/C To The Max Performance?

Sat Feb 12, 2011 1:49 am

If you mean maximum structural takeoff weight limits that is simply not true. MTOW is affected by alot of factors not the least of which is Landing weight. I can have a 737 structurally capable of taking off at 79015kg with a MTOW for a given flight of 72000kg or lower because to take off with more weight than that would put the plane over the maximum landing weight on arrival. I guarantee that over 90% of the flights I dispatch are landing weight limited not structural takeoff weight limited.

Quoting 9V-SPJ (Reply 14):
As everyone has said, payload is the key here, but sometimes, you may want to carry fuel in place of pax to reach your MTOW.

That makes no sense to me. Why would I carry a kilo more than I have to? That's just wasting fuel and putting me closer to my landing weight limit on arrival.
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Flighty
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RE: Do Airlines Use Their A/C To The Max Performance?

Sat Feb 12, 2011 3:58 am

Quoting YYZatcboy (Reply 15):
Why would I carry a kilo more than I have to? That's just wasting fuel and putting me closer to my landing weight limit on arrival.

Probably was referring to displacing cargo and leaving it behind, when it puts you over MTOW. Obviously, you won't just offload fuel to keep under the limit. Unless you were tanking extra fuel or something. But you are right, it was kind of said backwards.

That's another thing... presumably airlines do tank fuel around, and the MTOW must often figure into how much fuel they can carry.
 
tdscanuck
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RE: Do Airlines Use Their A/C To The Max Performance?

Sat Feb 12, 2011 5:50 am

Quoting YYZatcboy (Reply 15):
That makes no sense to me. Why would I carry a kilo more than I have to?

Several airlines ferry fuel on shorter segments because the cost of carrying the extra fuel is less than the extra cost of getting fuel at the outstation.

Tom.
 
YYZatcboy
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RE: Do Airlines Use Their A/C To The Max Performance?

Sat Feb 12, 2011 4:02 pm

Tom,

Yes Tankering fuel does happen, but that I would consider as a required fuel load, not putting on extra fuel for the sake of raising my TOW.
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9V-SPJ
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RE: Do Airlines Use Their A/C To The Max Performance?

Sun Feb 13, 2011 4:26 pm

Sorry for my ambiguous statement! I think I meant to say cargo, but yes, tankering fuel is also a possibility to raise TOW. SIA used to do it on the now defunct SIN-TPE-LAX leg.

9V-SPJ
 
YYZatcboy
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RE: Do Airlines Use Their A/C To The Max Performance?

Sun Feb 13, 2011 10:17 pm

My point still stands.

If I'm going YYZ-POP with a full load of Pax I am likely to have lots of room to reach the max takeoff (structural) weight of 79015kg, but I can only take about 1500 more kg before i hit my landing weight limit. I can take all the cargo or extra gas I want to out of YYZ because the plane can take off with it no problem, but at that point I would not be able to land in POP because I would be over the max structural landing weight limit when you factor in my reserve fuel and my alternate fuel. It is the same reason I can never carry YUL as an alternate for YYZ if i have a full load of pax, even if I tech stop in BUF because the plane cant land with that payload and still have enough gas to make it to YUL without breaking my Landing weight limit.

I'm not going to raise TOW for the sake of it because eventually it will eat into my fuel load or put me over my landing weight limit.
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